An impact event is a collision between celestial objects causing measurable effects. Impact events have physical consequences and have been found to regularly occur in planetary systems, though the most frequent involve asteroids, comets or meteoroids and have minimal impact. When large objects impact terrestrial planets like the Earth, there can be significant physical and biospheric consequences, though atmospheres mitigate many surface impacts through atmospheric entry. Impact structures are dominant landforms on many of the System's solid objects and present the strongest empirical evidence for their frequency and scale. One of the best-known recorded impacts in modern times was the Tunguska event, which occurred in Siberia, Russia, in 1908.